Hypoxia-inducible factor (HIF) is a heteroduplex, with α and β subunit. The beta subunit is usually present in excess, while the alpha subunit is the limiting factor in the formation of the functional dimer. The HIF-α subunit binds with the β subunit in the nucleus and, with the cooperation of cofactors, binds to DNA sequences called hypoxia response elements, and hence induces expression of target genes. There are three isoforms of the α subunit, HIF-1α, HIF-2α and HIF-3α. The activity of HIF is regulated via hydroxylation at two proline residues by an oxygen-sensitive family of prolyl hydroxylase enzymes (PHD), known as PHD1, PHD2 and PHD3. Hydroxylation at one or both of these proline residues allows binding of HIF-α first by the von Hippel-Lindau tumor suppressor protein (pVHL) and then by ubiquitin ligase which results in rapid ubiquitination and proteosomal degradation. The HIF-α subunits are also regulated by hydroxylation at a C-terminal asparagine residue by factor inhibiting HIF (FIH), an oxygen-dependent hydroxylase enzyme. Factor inhibiting HIF prevents the recruitment of transcriptional coactivators, thereby blocking the activity of HIF.
Under normoxic (oxygenated) conditions, HIF-1α is rapidly degraded, while under hypoxic conditions, HIF-1α is stabilized due to hypoxia mediated reduction of PHD and FIH activities and is translocated into the nucleus, where it dimerizes with the constitutively expressed HIF-1β, thereby inducing the expression of several genes including glucose transporters, glycolytic enzymes, angiogenic growth factors, and several molecules involved in apoptosis and cell proliferation such as erythropoietin (EPO), transferrin, endothelin-1, iNOS, heme oxygenase 1, VEGF, IGF and IGF-binding proteins.
The oxygen sensitive PHD family is also dependent on the presence of ferrous iron, ascorbate and the citric acid cycle intermediate, 2-oxoglutarate (2OG). HIF activity, therefore, depends on oxygen concentrations, accessible iron and glucose metabolism through its regulation by FIH and PHD.
Inhibition of HIF prolyl hydroxylases and HIF asparagyl hydroxylases thus provides a powerful approach for oxygen-independent activation of HIF. Such HIF activation by pharmacological means results in enhanced expression of genes as described earlier which perform multiple functions to recover from hypoxic/ischemic conditions. Therefore, HIF activation can offer significant therapeutic benefits in various disease conditions such as anemia of various types and tissue injuries caused by hypoxia/ischemia in conditions like acute kidney injury, myocardial infarction, stroke, hepatic ischemia-reperfusion injury, peripheral vascular diseases and transplantation of liver and kidney.
Hb (Hemoglobin) is an iron-containing metalloprotein in red blood cells (RBCs) that delivers oxygen. Decreased Hb levels resulting from anemia can lead to hypoxia in various organs and, therefore, cause patients severe clinical complications, such as severe fatigue, dyspnea, heart problems, nerve damage, impaired mental function and even death. The cause of anemia is multifactorial: blood loss, increased RBC destruction (e.g., hemolytic anemia), and decreased or faulty RBC production (e.g., iron deficiency and sickle cell anemia). 80% of patients with chronic kidney disease (CKD) develop anemia because of decreased production of erythropoietin (EPO) in the kidney. EPO is an essential growth factor that stimulates the erythropoiesis, and maintains their viability. Patients with rheumatoid arthritis, chronic inflammatory and infectious disorders, chronic heart failure, and cancers or who are undergoing chemotherapy often become anemic due to deficiency of EPO production.
The current treatment for anemia in chronic diseases, including anemia of chronic kidney disease, is iron repletion and treatment with EPO or its analogs. In addition to the high cost of EPO and its analogs, there are several shortcomings to this approach. First, these must be injected subcutaneously or intravenously, making administration more difficult. Second, there is a significant proportion of patients resistant to therapy with EPO or its analogs. Treatment of anemia with HIF-hydroxylase inhibitors may bypass EPO resistance, through effects on iron metabolism, and avoid the increased death and cardiovascular events associated with supraphysiologic levels of EPO.
Compounds which provide a means for inhibiting HIF hydroxylases and thereby activating the HIF, leading to enhanced expression of the various genes including EPO, vascular endothelial growth factor (VEGF), adrenomodulin etc. are therefore expected to be useful in treating various disorders including anemia of different types and conditions associated with ischemia/hypoxia.
EP661269 discloses substituted heterocyclic carboxamides of the following general formula and their use as inhibitors of prolyl-4-hydroxylase and as inhibitors of collagen biosynthesis.

WO2004108681 discloses isoquinoline derivatives and their use in increasing endogeneous erythropoetin.
WO2007070359 discloses quinolone based compounds of the following general formula exhibiting prolyl hydroxylase inhibitory activity and uses thereof.

WO2008076425 discloses azaquinolone based compounds of the following general formula exhibiting prolyl hydroxylase inhibitory activity and uses thereof.

WO2011007856 discloses certain triazolopyridine derivatives of the formula below as prolyl hydroxylase inhibitors and erythropoetin production inducers.

WO2012106472 discloses following napthyridine derivative based compounds as inhibitors of HIF hydroxylase.

WO2013043621 discloses substituted certain pyrimidines compounds which are useful as HIF prolyl hydroxylase inhibitors to treat anemia and like conditions and having the following general formula.

However, none of these compounds have reached the market and looking at the significant unmet medical need for such compounds based on their potential beneficial effects as discussed above, there is a need for identifying further compounds which can act as prolyl hydroxylase inhibitors. We herein disclose novel compounds which are expected to act as such inhibitors.